https://mikebeach.org/2011/07/26/how-to-monitor-your-microphone-through-headphones-in-ubuntu/
This walks you through routing the microphone's audio to your headphones. I've tested it on a Raspberry PI (Raspbian Jessie).
pulseaudio -D
pactl list sources short
Then copy the appropriate source device to your clipboard. In my case: alsa_input.usb-0d8c_C-Media_USB_Headphone_Set-00-Set.analog-mono
pactl list sinks short
In my case: alsa_output.usb-0d8c_C-Media_USB_Headphone_Set-00-Set.analog-stereo
Edit the names of input and output to the appropriate source and sink and run the command:
pacat -r --latency-msec=1 -d alsa_input.usb-0d8c_C-Media_USB_Headphone_Set-00-Set.analog-mono | pacat -p --latency-msec=1 -d alsa_output.usb-0d8c_C-Media_USB_Headphone_Set-00-Set.analog-stereo
Whatever you say or record through your mic jack will now be output to your headphones. Enjoy!
It's been a while since the last comment, but I just now stumbled on this while trying to figure something out. Going to post what I've done in case that helps.
I was originally using a pipeline like above to get audio from my capture card routed to my headphones. I was able to tune different options to get rid of the static, but was occasionally having lag issues.
I'm now using a gstreamer pipeline that looks like this: